This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for APPARATUS FOR SHADING CORRECTION IN IMAGE SCANNING SYSTEM AND METHOD THEREFOR earlier filed in the Korean Industrial Property Office on the 26th of May 1998 and there duly assigned Ser. No. 19031/1998.
1. Field of the Invention
The present invention relates to an apparatus and a method for shading correction in an image scanning system. More particularly, the present invention relates to an apparatus and a method for shading correction in an image scanning system for informing a user of any presence of errors of shading correction above predesignated allowable values by performing shading correction using correction shading data stored in a non-volatile memory, for adjusting the image quality, and preparing periodically determination shading data to determine the maintenance time for cleaning and fixing in the image scanning system.
2. Description of the Related Art
An image scanning apparatus such as a scanner is a widely-used means for scanning printed materials, photographs, letters or drawings made by hand, etc. into color or black-and-white images, and is one of the main components of a multi-function peripheral (MFP), a translator for documents, a computer for computer aided design (CAD), facsimile, a character recognizer, a digital copier, etc.
The demand for office equipment such as a digital copier, a printer, a scanner, and a fax machine, etc. becomes greatly increased owing to the development of office automation, and also, the technology for each office equipment is highly-improved in order to maximize its function for office automation.
Of the equipment, a multi-function peripheral (MFP) recently represents the above-described high-development of office automation, and the MFP is a system made by integrating multiple pieces of the above equipment, which were used respectively with their own function thereby reducing the financial cost, and saving space for installation. Also, the MFP has a function of outputting documents. In addition, the MFP is one of the representative systems to employ an image scanning system such as a scanner.
In other words, the MFP is a system capable of outputting documents in multiple ways, i.e. it can print the data transmitted from a host computer, read a document as an image as a scanner, print and copy the scanned image document, transmits the image document to far-away distant places through a communication path as a facsimile, etc. That is, it is a multi-functional terminal system to integrate a facsimile, a scanner, a printer, a copy machine, etc. which were single equipment, respectively. Also, it has a host computer-interface function to communicate with a host computer.
As described above, referring to the MFP as an example, there are various types of products being widely-used and commercially-available, and having multi-functions by means of the integration and the linkage connection of related equipment with the scanner as a basic component. The xe2x80x9cimage scanning systemxe2x80x9d referred in this application relates to equipment having the image scanning function. In this regard, the present invention is directly related with the technology of performing shading correction in the above described image scanning system.
In a typical image treatment in general, xe2x80x9cshadingxe2x80x9d is a phenomenon present in an image pickage tube such as vedicon, cathode ray tube(CRT), etc., wherein the output from, for example, a CRT is not uniform, and so, the light density produced from the output image is different according to the portions. The shading is attributed to some reasons, such as non-uniformity of a target, or redistribution of secondary electrons on the target.
The distorted image can be adjusted using an adjustable electron lens. Recently, shading is also cited in relation to an image input system, such as the image scanning system, broader from the above display device, and xe2x80x9cshading correctionxe2x80x9d refers to image treatment methods to remove the shading phenomenon and improve the distorted image.
In other words, the shading correction is to adjust the darkness or the uneven distortion of the image on a screen in the peripheral edge portion because of the characteristics of the optical mechanism when producing a digital image for a computer by digitalizing general documents, photographs, etc. The shading correction can be made by adjusting the light density, i.e. divide the screen into a number of small areas, determine a conversion function of density for each divided area, and adjust the density such that the image produced on the whole screen has identical light intensity. The shading correction can also be performed by achieving shading data during dummy scanning.
A shading correction apparatus of an image scanning system exemplary of contemporary practice is the art will now be discussed.
First, light emitted from a lamp scans a document. During the scanning step, the light is reflected on the document and is then focused into a optical module. An image sensor which includes image sensors which can sense three primary colors, red(R), blue(B), and green(G), respectively, receives the light irradiated from the optical module by a lamp and changes the light inputted from the optical module into an analog image signal. The image sensor is driven according to a sensor driving clock provided from a scanning controller so as to generate the output of the number of pixels according to the resolution of each image sensor.
The scanning controller controls a lamp driver such that light emitted from the lamp is irradiated on a document and the light reflected from the document is then input into the image sensor via selected paths. Depending on properties of the color image sensors, the input light of the image sensor is converted into an analog image signal which is proportional to light intensity as input, and is output to an analog/digital converter.
Then, the analog/digital converter converts the analog image signal having respective color elements output from the image sensor into a digital image signal having a preset number of bits for each color component.
A shading memory stores shading data corresponding to the digital signal converted from the analog signal of color elements respectively at the corresponding addresses of each color element and each pixel by scanning a shading reference pattern during performing of pseudo scanning and then color-separating. The shading memory also stores a shading factor matrix input from a shading correction controller corresponding with each of the color elements and each of the pixels.
The shading correction controller reads the shading data stored in the shading memory, based on the addresses respectively during the pseudo scanning, achieves a shading factor matrix corresponding to each color element and each pixel by counting the preset maximum light value (M) by the unit of pixels, and supplies the matrix to the shading memory. During performing of the real scanning, the shading correction controller controls the shading memory such that the shading factor matrix stored in the shading memory is output corresponding to each of the color elements and each of the pixels.
A shading corrector corrects the digital image data of each color element output from the analog/digital converter from the shading factor matrix output by the control of the shading correction controller during the real scanning, and then outputs the corrected digital image data, resulting in obtaining digital image data whereby the output deviation among respective color elements is corrected.
Generally, any type of image scanning system might produce great deviation due to various reasons such as the characteristic differences of light reaction, technical differences in the optical mechanism, etc. Preferable ways to solve the problem are to correct the deviation in view of the mechanical system with the assembly completed. However, sometimes, the above access is difficult or impossible technically in many cases. Thus, the shading correction is to solve the above problem by image-treating.
Moreover, the shading factor matrix typically is the most important factor to determine the characteristics of the shading correction, and the shading factor matrix is achieved by pseudo scanning, which refers to scanning a shading reference pattern, such as a white plate and a white paper displaced facing the image sensor, or a white roller.
The shading reference pattern should have the same optical density as that of the white regions of the shading reference pattern. Especially, in a case of using the white roller as a shading reference pattern, there can occur a deviation of an optical amount, which is attributed to the changes of image input distance because a document is supplied between the shading reference pattern and the image sensor. In case of the roller, it should be assembled to be exactly aligned in an image sensing line because it also does document driving and, if the shading reference pattern is contaminated due to the friction with the document, the shading factor matrix should be renewed every time when checking the contamination, which can thereby deteriorate the quality of the image reproduction.
The present invention is intended to solve the above-described problems and provide a shading correction apparatus of an image scanning system and a method for shading correction in the image scanning system of the present invention.
One object of the present invention is to provide a shading correction apparatus of an image scanning system and a method therefor for the purpose of improving the image quality associated with various types of scanning systems by performing shading correction using correction shading data stored in non-volatile memory, and complying with the maintenance time by properly using periodically-prepared maintenance shading data to determine the maintenance time, and comparing whether there occurs a shading correction deviation above a certain allowed value.
Another object of the present invention is to provide a shading correction apparatus of an image scanning system and a method therefor to thereby provide optimized image quality by removing the image distortion due to the distance between a shading reference pattern and a document and an optical density deviation of the shading reference pattern, to promote reducing expenses due to the improvement of preciseness of the shading reference pattern (i.e. contact, flatness, optical density of white, etc.), and to promote avoiding difficulties of exactly aligning a center line of a white roller to the image sensing line during assembly of components in case of the system using a shading reference pattern of white roller type.
To achieve these and other advantages and in accordance with the purpose and the advantages of the present invention, a method for shading correction of an image scanning system to read image data of a document by photoelectric conversion is provided by the present invention. The method includes preparing the shading factor matrix by scanning a standard shading reference pattern, such as white paper at the time of product production, which is stored in a non-volatile memory without the periodically-carried out pseudo scanning, and using the shading factor matrix, shading correction is performed in a real scanning. Also, a shading correction apparatus of the present invention includes a means for detecting/informing of the contamination/damages of the optical parts of the system so as to automatically detect any negative changes of the characteristics of the optical parts, and the shading factor matrix is renewed in a case of cleaning the fouled optical parts or fixing them with notice of the maintenance time.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.